Since WWII the MI4 Aiming Post Light has been used for artillery and mortar operations to maintain orientation despite possible movement of the gun when fired. Each light consisted of two size D flashlight batteries in a brass case having an on-off switch, an incandescent bulb and a reflector/lens filter. To avoid confusion, half the lights have a red filter and half have a green filter. Each howitzer or mortar uses one of each. They presently cost over $25 each.
Aiming post lights are placed forward of their guns a distance from 50 to 100 meters. They drain the batteries in a night or so and require replacement, sometimes a hazardous task, particularly when the enemy is close by. Obviously an aiming light that will survive an engagement without replacing batteries is preferred.